Japanese Laid-Open Patent Application Nos. 2005-225043 and 2005-224101 disclose image forming apparatuses in which an image is formed on a sheet having an RFID tag, which is a small device capable of receiving, storing, and transmitting data using a radio wave. FIG. 1 schematically depicts the apparatus of the former publication. An RFID reader/writer 200 is located upstream of a print head 300 along a transport path, which starts with a feeding tray 100. Data is read or written from or into the RFID tag in a region at the RFID reader/writer 200 in which communication between the RFID tag and the RFID reader/writer 200 is enabled (to be hereafter referred to as a “communication-enabled region”). The speed at which the sheet is transported is changed, or the sheet is stopped, to enable the reading or writing of the data.
The RFID reader/writer 200 is disposed preceding the print head 300 because the RFID tag should be read before the sheet is printed by the print head 300. Depending on the orientation of the sheets as they are placed on the feeding tray 100 by a user, the RFID tag, which may be disposed at any of the four corners of the sheet, may be located at the leading end or trailing end of the sheet with respect to the sheet transport direction. When the RFID tag is located at the leading end, the tag reaches the RFID reader/writer 200 before the print head 300, so that the RFID tag can be read before the sheet is printed by the print head 300. However, when the tag is located at the trailing end, the sheet may already be printed by the print head 300 when the RFID tag reaches the RFID reader/writer 200. Because the RFID tag is read using an electromagnetic wave, the RFID reader/writer 200 can read the RFID tag even at some distance. However, the electromagnetic wave used is weak and the operable distance is limited, so that the sheet may be printed a little by the time the reading of the RFID tag is completed.
This publication, i.e., Japanese Laid-Open Patent Application No. 2005-225043, teaches that a fixed speed is set in advance for an adjusted-speed operation in which the sheet transport speed is adjusted (typically reduced), to allow for accessing the RFID tag. However, in this case, if the fixed speed that is set in advance is inappropriate, an error may occur. More specifically, in this image forming apparatus, the speed at which the sheet passes the RFID reader/writer 200 or the duration of time in which the sheet is stopped to enable the reading or writing of the RFID are set such that, to stay on the safe side, more time is provided than is actually minimally required. Thus, the apparatus does not allow the transport speed to be varied depending on the communication speed of the RFID tag on a real-time basis. As a result, the conventional technology is unable to fully reduce the time required for the sheet to pass the RFID reader/writer.